Sorting methods



sept. 19, 1961 G. P. coPPlNG 3,000,498

SORTING METHODS Filed May 19, 1958 4 Sheets-Sheet 1 EOFFREY F Ca/P//YG' INVENTQR Y/L, 16m/AL 16M Sept 19, 1951 G. P. coPPlNG 3,000,498

SORTING METHODS Filed May 19, 1958 4 Sheets-Sheet 2 7 /L-G. 3. fof/CEK Pfaff/w.

lNvENToR BY A ATTORNEYS Sept. 19, 1961 G. P. coPPlNG 3,000,498

SORTING METHODS Filed May 19, 1958 4 Sheets-Sheet 3 8. INVEN-ron A TTQQNEYS Sept. 19, 1961 G. P. coPPlNG 3,000,498

soRTING METHODS Filed May 19, 195e 4 sheets-sheet i B WM WM;

Aw--r oRNEYS United States Patent O 3,000,498 SORTING METHODS Geoffrey Percy Copping, Chesham, England, assignor to Her Maiestys Postmaster General, London, England Filed May 19, 1958, Ser. No. 736,071 Claims priority, application Great Britain May 20, 1957 15 Claims. ((1209-81) The present invention relates to the handling of letters and other fiat articles and has for an object to provide an improved method of handling letters or similar articles.

In the handling of letters and like postal items it is necessary, prior to stamp cancellation, to face the letters, i.e. to arrange them so that the stamps of all the letters are similarly positioned with respect to a fixed reference point, and in the sorting of letters by means of sorting machines, such facing of the leters ensures that the letters are presented with the address side of the letter facing the operator of the machine and correctly positioned for reading the address.

'Ihis preliminary facing of the letters is usually effected by detecting the stamps on the letters, the letters being manipulated to bring the stamp or stamps to substantially the same relative position on each letter.

It has heretofore been proposed to detect the stamps by relying on the difference in the colour and intensity of light reflected from the surface of the letter envelope and that reflected from the stamp but this has not proved entirely satisfactory as in some cases the colour of the stamp and that of the envelope are not suii'iciently differentiated to provide an easily measurable difference in the light reflected.

|It has also been proposed to provide the stamps with an electrically conductive backing which can then be detected by capacitance measurement, or with a coating of magnetic dust which is4 detected by electromagnetic means. Either of such methods involves fundamental changes in themanufacture of the stamps which is undesirable and the effect on the appearance of the stamp is a further undesirable feature.

According to the present invention, -a method of handling letters and similar ilat articles includes the step of detecting by electrical means an electrically conducting substance carried by an unexposed surface of the letter or similar article.

Conveniently, the presence of the electrically conducting substance is detected by causing the letter or other -liat item to pass beneath and in engagement with a pair `of spaced electrodes connected to an electric supply whereby, when the electrically conducting substance passes beneath the electrodes, current is caused to ilow therebetween.

In the case of letters and similar at postal items, the

electrically conducting substance may be carried by the postage stamp or stamps axed thereto.

, Inconsidering possible methods of applying an electrically conducting substance to a postage stamp an essential condition to be observed is that the appearance.

of the stamp must be unaffected, i.e. the substance must be substantially invisible to the naked eye when the stamp..is secured on the" letter.

In addition the electrically conducting substance should` Patented Sept. 19, 1961 ICC the stamp lin order to avoid impairing the appearance of the stamp.

One substance which can be applied readily and cheaply by means of a printing technique is a graphite-base ink, but owing to the dark colour of the ink the application of the substance to the rear surface of the stamp must be limited to those portions of the stamp which are strongly coloured or heavily printed so that the dark colour of the graphite-base ink is not visible through the stamp.

It is therefore proposed to apply the electrically conducting substance in one or more thin lines extending across the rear surface of heavily coloured portions of the stamp, the possible number of lines, of course, depending on the design and colouring of the stamp. It would be desirable to provide one line for each unit of value of the stamp, so that in addition to detecting the presence of the stamp the value thereof could also be detected and it will be possible to discriminate, for example, between fully paid and deferred mail.

Accordi-ng to a further feature of the invention, therefore, there is provided a postage stamp having printed on the rear surface thereof one or more lines of an electrically conducting substance.

Conveniently the electrically conducting substance is applied in the form of a graphite-base ink prior to applying the gum to the rear surface of the stamp, and a suitable ink for this purpose is a colloidal graphite dispersion known as Dispersion 1298 and sold under the registered trademark dag The detection of the conducting lines on the rear surface of the stamp by spaced contact members engaging the front surface of the stamp is achieved by applying to the contact members a voltage sufficient to cause a discharge between the electrodes when a conducting path is present on the rear surface of the stamp, the discharge following a path from one contact member through the paper of the stamp, along the conducting path and back through the paper of the stamp to the other contact member. The discharge may be caused to operate apparatus controlling the further movement of letters and/or a counting device for registering the number of discharges for each letter.

The invention will now be described with reference to the accompanying drawings in which:

`FIGURE 1 is -a rear View of a postage stamp having applied thereto an electrically conducting substance according to the invention;

FIGURE 2 shows diagrammatically in plan view one form of detecting apparatus suitable for carrying the invention into effect;

FIGUR-E 3 is a section taken along the line IIl-III of FIGURE 2;

yFIGURE 4 is a circuit diagram of one form of detector circuit for use with the detecting apparatus of FIGURES 2 and 3;

FIGURE 5 is a plan view of a composite sensing roller suitable for use in carrying the invention into effect;

FIGURE 6 is an end elevation of the composite sensing roller of FIGURE 5 and including a cooperating driven roller; and

FIGURES 7 to- 11 respectively illustrate alternative forms of detector circuits for use with the sensing roller of FIGURE 5.

As will be `seen in FIGURE l, a postage stamp 1 has applied thereto two thin lines 2 of an electrically conduotingsubstance. The said lines are applied by printing with a graphite-base ink prior to applying the gum to the rear surface of the stamp and are positioned respectively adjacent each longitudinal side edge of the stamp so as to lie under the heavily coloured edge porf tions of the stamp. As hereinbefore stated, the number of lines may be varied and, for example, there may be only one line or, if the design and colouring of the stamp permit, more than two lines, and in order to allow for cases in which the stamps are affixed to the letter in a horizontally extending position further lines 3 may be provided extending transversely of the stamp along one or both edge portions thereof.

Referring now to FIGURES 2 and 3, a device for detecting the conducting lines on the stamps includes driven rollers 4 co-operating with free running springbiased rollers 5 for feeding a letter 6 through the device. Positioned intermediate the driven rollers 4 is a further driven roller 7 which serves to support the letter against pressure exerted thereon by a sensing device in the form of a pair of rolling electrodes 8 supported at one end of a pair of arms 9 pivoted as at 10 and spring-loaded in a direction towards the letter, the electrodes thus being pressed into engagement with the surface of the letter. As will be seen more clearly in FIGURE 2, each electrode 8 comprises a disc-like member rotatably supported in one of `the arms 9 and the edge of the disc is chamfered to provide a sharp edge engaging the surface of the letter. Electrical connection to the disc is made by means of a spring-loaded brush 11 and a exible connecting wire 12 adapted to make connection with a suitable detector circuit. One form of detector circuit is shown in FIGURE 4 in which electrodes 13--corresponding to the discs 8 of FIGURES 2 and 3-are shown connected respectively to a high impedance supply 14 of 3,000 volts and through a resistor 15 to negative high tension. The lower electrode 13 is also connected to the grid of a triode 16 the anode of which is connected through a resistor 17 to 100 volt positive high tension, and also through a capacitor 18 to a device 19 which may be an electronic counter or an electromagnetic letter processing control device.

In operation of the detector circuit there will be a variable resistance between the electrodes 13 varying from the surface resistance of a letter passing under the electrodes to the much lower resistance of the ionized path through the paper of the stamp and along a conducting line printed thereon, so that each time a conducting line passes under the electrodes an impulse will be applied to the device 19 to actuate the counter or the letter processing control.

In the application of the invention to letter sorting, it has been found necessary for the detecting apparatus to be capable of detecting a stamp placed anywhere within a 2 inch wide strip at the upper edge of a letter and in FIGURES 5 and 6 there is shown an alternative construction of sensing device which is in the form of a composite sensing roller formed by a plurality of metal discs assembled together with electrically insulating rings interposed therebetween. Thus, in the sensing device of FIGURE 5 there are six such metal discs 20 separated one from another by electrically insulating rings 21. Conveniently, the discs 20 are made of brass and have a thickness in the neighbourhood of 1/16 inch, each disc being cylindrical in contradistinction to the disc-like electrodes 8 of FIGURE 2 which have chamfered edges. The rings 21 may be formed of Perspex and may have a thickness of approximately l/s inch.

The letters are supported on one long edge for feeding past the composite sensing roller which is spaced 1/2 inch above the support for the long edge of the letters so that a stamp positioned anywhere within a 2 inch wide strip extending along the said long edge will be engaged by at least two of the sensing discs of the roller.

The discs 20 and rings 21 are assembled upon a shaft 22 at each end of which there is mounted an assembly of slip rings 23 and electrically insulating spacers 24, there being four slip rings at one end of the shaft and two at the other. Each slip ring is electrically connected as indicated in broken line at 25 to one of the discs 20 and carbon brushes 26 engage the respective slip rings to enable electrical connection to be made with the corresponding discs.

The composite sensing roller is supported in a convenient manner for engagement with a driven roller 27 (FIGURE 6) and is spring-loaded in the direction of the roller 27. The roller 27 is formed of or incorporates a resilient material so that the periphery of the roller yieldingly engages the sensing roller and in this manner there is a slight wrap-round of a letter 28 passing through the rollers. This wrap-round gives an area of contact of the discs 20 upon the letter instead of a line Contact as in the arrangement of FIGURE 2 and ensures detection of an electrically conducting line on a stamp which is not squarely placed on the letter. However, the angle of wrap-round indicated by rp in FIGURE 6 and shown in exaggerated form must be care fully related to the spacing of lines on the stamps in the case in which more than one line is employed to ensure that two adjacent lines are not simultaneously engaged by the discs 20 and therefore would register as one line.

Connections are taken from the brushes 26 to a detecting circuit or circuits as will hereinafter be more fully described and one way of connecting the discs would be to connect alternate discs together so that the ve gaps between the discs would appear in parallel. This method of connection is satisfactory for use with dry envelopes, the surface of which provides a resistance between each pair of discs which is of the order of megohms cornpared with about 4 megohms corresponding to the resistance of an z inch length of graphite line between two adjacent discs, and two spark discharge paths through the paper of the stamp. However, in wet weather the envelopes may become very damp and the surface resistance between each pair of discs may drop to 10 megohms or less, so that the resistance of the ve gaps in parallel would be less than that of the graphite line and spark discharge paths.

It is therefore preferred to connect the electrodes as shown in FIGURE 7, in which one side of a high impedance source 29 of extra high tension, for example from 2.5 to 3 kv., is connected to the brushes 26 of alternate discs 20 through resistors R1 individual to each disc. Each of the brushes 26 corresponding to the discs 20 intermediate the said alternate discs is connected to the other side of the high tension supply 29 through a fixed resistor R2 and a variable resistor R3. The junction of the resistors R2 and R3 in each case is connected to the input of a trigger circuit adapted to give an output when current ows from one of the said alternate discs to an intermediate disc, there being thus three such trig- -ger circuits and the outputs are commoned for connection to counting and/or letter processing control means.

The trigger circuit is shown enclosed in the broken line rectangle 30 and conveniently takes the form of a Schmitt trigger circuit, as described in volume 15 (1938), page 24 of the Journal of Scientic Instruments. The said circuit comprises a rst valve V1, the grid of which is connected to the input of the trigger and is normally held at earth potential through the resistor R3 so that the valve is cut-oi. When the resistance between the sensing discs falls the current through resistor R2 and R3 increases and raises the potential of the grid of valve V1 until a point is reached, depending on the adjustment of the resistor R3, at which the valve V1 conducts and the trigger operates to produce a square pulse of fixed amplitude at the output.

When the paper of the stamp breaks down and current flows from one disc to an adjacent disc through the graphite line, two spark discharges occur and these include high frequency components which can be distinguished from the single change of potential at the junction of resistors R2 and R3 caused by the incidence across the detecting discs of a damp or slightly conducting surface, in which case no spark discharge occurs. Thus, in

the circuit of FIGURE 8 use is made of these high frequency components to operate a single trigger circuit by coupling the junction of resistors R2 and R3 to the input of the trigger circuit through a capacitor C1 of very small capacitance of the order of 47 mmf., resistors R9 and R being interposed between the capacitor C1 and the input of the trigger circuit to determine the operating point of valve V1, sensitivity control being obtained by adjustment of resistor R10 or resistor R3. In FIG- URE 8 only one pair of sensing discs is, shown but it will be understood Ithat similar connections of `the other pairs of sensing discs to the junction of resistors R9 and R10 will be made.

An alternative method of utilising the high frequency components of the spark discharge to actu-ate the trigger is shown in FIGURE 9, in which there is employed a transformer T interposed between the sensing discs and a single trigger circuit 30, the transformer hav-ing three similar input windings L1 and a single output winding L2. Each of the input windings L1 is shunted by a capacitor C3 to form a tuned circuit and the output winding L2 is likewise shunted by a capacitor C2 to provide a tuned circuit one side of which is connected through a variable resistor R11 to earth and the other side to the input of a single trigger circuit 30.

In order to improve the discrimination between damp or slightly conducting surfaces of a letter and a postage stamp atirred thereto, an integrating circuit may beincluded between the sensing discs andthe trigger circuit. One such arrangement is shown in FIGURE l0 in which the said integrating circuit is formed by a capacitor C4 and a rectiiier X1 shunted by a resistor R12, the circuit otherwise corresponding to the circuit of FIGURE 8. The circuit of FIGURE 10 is arranged so that the capacitor C4 charges partially during the positive half cycle of the high frequency discharge and therefore in order to operate the trigger circuit several cycles of high frequency are needed to charge the capacitor C4 to the triggering level of the valve V1 of the trigger circuit. Thus, a single change of potential at the junction of resistors R2 and R3 caused by the incidence of a damp or slightly conducting surface is not sufficient, in itself, to operate the trigger circuit.

In yet a further method of utilising the high frequency components of the spark discharges a high frequency probe is positioned between adjacent discs-as shown in broken line at 31 in FIGURES 5 and 6. As shown in FIGURE l1 the probes 31 are connected in parallel to the input of a single trigger circuit and to a tuned circuit L5C5 so that the trigger circuit is operated upon a spark discharge occurring from the sensing discs through the paper of the stamp.

Although the above described specific embodiments of the invention refer to letters carrying adhesive postage stamps aixed thereto, it will be appreciated that the invention could similarly be applied to envelopes having stamps printed or embossed thereon, or folders or other similar paper items by means of a suitable arrangement of electrically conducting lines applied to an unexposed surface thereof.

I claim:

l. A method of handling letters and similar flat articles having an electrically conducting substance applied thereto and a di-electric material shielding the said substance, the said method including the step of detecting the said conducting substance by `applying to the said shielding material at spaced points thereon, an electric potential of suticient voltage to cause a discharge through the di-electric material to the electrically conducting substance, thereby to establish an electrical connection between the said spaced points.

2. A method of handling letters having adhered thereto a postage stamp provided on its rear surface with at least one line of an electrically conducting substance which comprises applying to the front of `the postage stamp at points spaced along the line of said conducting substance, an electrical potential of suflicient voltage to cause a discharge through the paper of the postage stamp to the line of electrically conducting substance, thereby to establish electrical connection between said spaced points and causing the flow of electric current resulting from said connection to operate letter handling devices.

3. A method of handling thin sheet articles having applied to one surface thereof, an electrically conducting substance, which includes the step of applying to the other surface at spaced points thereon, an electric potential of sufficientvoltage to cause a discharge through the material of thesheet to the said electrically conducting 'substance, and causing the ow of electric current resulting from said discharge to operate sheet handling devices.

4.- Apparatus for handling letters and sirnillarflat articles having applied thereto an electrically conducting substance and a di-electric material shielding the said substance, comprising at least two electrodes, means for feeding the letters or other articles past the said elec- -trodes -for engaging the di-electric material therewith so that the conducting substance extends transversely with respect to the electrodes, a source of potential connected to said electrodes and having a voltage sucient to cause an electric discharge from the electrodes through the said di-electric material to the conducting substance, and electric circuit means connected to the electrodes for detectingthe s aid electrical discharge.

5, Apparatus as claimed in claim 4, wherein thesaid electrodes comprise a plurality of spaced electrically insulated metal discs and means rotatably supporting said discs, the apparatus further comprising a driven roller for engaging the letters or other ilat articles with the discs :and means urging the discs towards the driven roller and into engagement with the di-electric material of a letter or other flat article engaged between the roller and the discs.

6. Apparatus for handling letters having adhered thereto a postage stamp provided at its rear surface with at least one line of an electrically conducting substance, comprising a multiplicity of spaced disc electrodes, a spindle supporting said disc electrodes, electrically insulated one from another, means rotatably mounting the said spindle, a driven roller mounted opposite said spindle for co-operating with said disc electrodes to yfeed a letter presented thereto past the electrodes so that a stamp on the letter is engaged by at least two adjacent discs, a source of electric high potential of a voltage sufficient to discharge through the paper of the stamp, means connecting one pole of said source to a multiplicity of rst resistive devices, means connecting each of said first resistive devices to alternate ones of said discs, a multiplicity of second resistive devices, means connecting said second resistive devices to the other pole of said source, means connecting each of said second resistive devices to a disc interposed between said alternate discs, whereby a spark discharge is produced from said discs through the paper of the stamp to the electrically conducting surface on the rear thereof, and means responsive to said spark discharge for controlling the operation of letter handling devices.

7. The apparatus las claimed in claim 6, wherein the said discharge lresponsive means comprises a multiplicity of trigger circuits, an intermediate tapping point on each of said second resistive devices, means connecting each said intermediate tapping point to a separate one of said trigger circuits, each said trigger circuit being operable to produce an output upon the flow of current from one disc to an adjacent disc, and means connecting together the outputs from the said trigger circuits for producing an out-put upon operation of at least one of the trigger circui-ts.

8. The apparatus as claimed in claim 6, wherein the said discharge responsive means comprises a multiplicity of separate means for selecting the high frequency components of spark discharges from the disc electrodes to the electrically conducting substance, an intermediate tapping point on each of said second resistive devices, means connecting each said intermediate tapping point to a separate one of said selecting means, a single trigger circuit, and means connecting all the said selecting means to the said single trigger circuit, thereby to produce an output from the trigger circuit upon spark `discharge from `an electrode to the electrically conducting substance.

9. The apparatus as claimed in claim 8, in which each said Selecting means comprises a tuned circuit.

'10. The apparatus according to claim 8 further comprising an integrating circuit, means connecting the integrating circuit to said selecting means and to the single trigger circuit so that several cycles of high frequency are required to produce an output from the trigger circuit.

11. The apparatus as claimed in claim 6, wherein the said discharge responsive means comprises a probe positioned between adjacent disc electrodes for detecting high frequency components of spark discharges from the disc electrodes, a tuned circuit connected to said probe, a single trigger circuit and a connection from the probe to the input of the trigger circuit.

12. In a method of handling letters as claimed in claim 2, the step of applying to the rear surface of said postage stamp at least one line of an electrically conducting substance.

13. A postage stamp having applied to the rear surface thereof at least one line of an electrically conducting graphite-base ink and a layer of water soluble gum overlying the rear surface of the stamp and the said line of graphite-base ink thereon.

14. A postage stamp according to claim 13, `having a plurality of said lines of the said electrically conducting graphite-base ink spaced `from one another, the number of lines being related to the value of the stamp.

15. A postage stamp for use in handling letters by sorting machines and the like comprising at least one line of an electrically conducting substance printed upon the rear surface thereof and a layer of water-soluble gum overlying substantially all of said rear surface, said conducting substance for `forming a portion of an electrical discharge path to provide information related to information printed upon the front surface of the stamp.

References Cited in the file of this patent UNITED STATES PATENTS 1,217,092 Hopp Feb. 20, 1917 2,158,749 Elliott May 16, 1939 2,171,556 Higginbottom et al. Sept. 5, 1939 2,254,931 Bryce Sept. 2, 1941 2,357,455 Bryce Sept. 5, 1944 2,502,785 Gottschalk Apr. 4, 1950 2,634,911 Wolowitz Apr. 14, 1953 2,697,514 Stahl Dec. 21, 1954 2,719,629 Robinson Oct. 4, 41955 

